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Cyanosis in late teens

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Q1: What is the most likely cause of the cyanosis?

A form of congenital cyanotic heart disease with a right to left shunt is the most likely cause of cyanosis in this case. Pulmonary causes for the cyanosis are virtually eliminated by the normal chestx ray and non-correction of hypoxia with 100% oxygen.

Q2: What does the transoesophageal echocardiogram show?

The TOE shows an abnormal connection (indicated by the arrow) between the left atrium and dilated right pulmonary artery. The cause of this patient's cyanosis is a left atrial to right pulmonary artery fistula.

Q3: What treatment options are available for this patient?

Several treatment options are available. Surgery can be undertaken to close the fistula by ligation or dissection, or it can be closed during cardiac catheterisation and pulmonary angiography by embolisation using a steel coil, umbrella, or detachable balloon.

Discussion

A fistula between the pulmonary artery and left atrium is a rare type of pulmonary arterio-venous malformation. It is, however, an important diagnosis to make as it can be corrected by simple surgical techniques, and the patient usually recovers to lead a normal life. The commonest causes of a pulmonary arterio-venous malformation are either that it is a congenital malformation or that it is associated with hereditary haemorrhagic telangiectasia.1 Acquired forms are either caused by trauma or are associated with juvenile hepatic cirrhosis, portal vein thrombosis, schistosomiasis, or metastatic thyroid carcinoma. Pulmonary arterio-venous malformations usually present in early adult life with the classic triad of cyanosis, clubbing, and polycythaemia with no cardiac murmur. In severe cases they occasionally present with cyanosis and heart failure in infancy. A few patients remain completely asymptomatic—mild desaturation by pulse oximetry may be the only finding. Pulmonary symptoms include breathlessness on exertion, haemoptysis, or thoracic pain. In some patients, neurological symptoms such as headaches, fits, speech disorders, or transient ischaemic attacks may dominate the clinical picture. Transient ischaemic attacks and stroke from paradoxical emboli may occur in up to 40–50% of patients.1 It is estimated that the annual risk of stroke in these patients is approximately 1.5%.2

Cardiac cyanosis (caused by a right to left shunt) is differentiated from pulmonary causes of cyanosis by there being no significant increase in Po 2 after inhaling 100% oxygen. Secondary polycythaemia may occur because of a compensatory increase in erythropoietin production. Other simple clues to aid the diagnosis include ECG findings of left axis deviation, left atrial enlargement, and left ventricular hypertrophy,3 4 and an opacity adjacent to the right border of the cardiac silhouette on chestx ray.3

To diagnose an atrial to pulmonary artery fistula, a high index of suspicion is required during echocardiography. The pulmonary artery may appear dilated and tortuous, and increased flow velocities may be seen on Doppler examination of the pulmonary veins. This is often difficult to detect, especially in smaller shunts, and this difficulty was seen in our case. TOE can be used as a supplementary investigation and has proved to be of great diagnostic value in many aspects of both paediatric and adult cardiology. Convention transthoracic echocardiography is limited by the poor tissue penetration of high frequency transducers (5 MHz). Adequate images can be sometimes difficult to obtain even with lower frequency transducers (2.25–2.5 MHz), and structures at the back of the heart (for example, the left atrium) can often be missed. Magnetic resonance imaging and computed tomography are considered supplementary investigations. TOE has an advantage over computed tomography and angiography, especially in children and adolescents, in that it involves no ionising radiation and is therefore safe for repeated use.

Learning points

  • Cardiac cyanosis (from a right to left shunt) can be differentiated from pulmonary causes of cyanosis by the fact that there is no significant increase in Po 2 with 100% oxygen.

  • Pulmonary arterio-venous malformations are relatively common causes of cyanosis in adolescence.

  • Pulmonary artery to atrial fistula is a rare type of pulmonary arterio-venous malformation.

  • The diagnosis of these lesions is important as they are easily treatable.

  • Conventional echocardiography can miss the diagnosis, and TOE may be used as a supplementary investigation.

References

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